1. Field of the Invention
This invention relates to modules useful in the collection and conversion of electromagnetic radiation and more particularly to an improved single reflection non-focusing optical module useful in apparatus for the collection of solar energy and the conversion of such energy into electrical and/or heat energy.
2. Description of the Prior Art
The recent emphasis placed upon fossil fuel conservation has resulted in a proliferation of apparatus for the collection and conversion of solar energy. The prior art devices generally have employed a solar collector having a reflective surface, usually in a generally parabolic configuration, for focusing the reflected energy onto a receiving surface either directly or through a folding optical system. Non-imaging optical collectors are also known, examples being found in U.S. Pat. No. 3,899,672 and in our own prior U.S. Pat. No. 4,131,485. Known folded reflective optical systems generally have employed a receiving surface disposed substantially perpendicularly to the optical axis of the collectors, particularly when the receivers are in the form of solar cells for converting the solar energy directly into electrical energy.
In the use of photovoltaic solar cells as the receiver for a solar collector, the solar energy collected from the large surface area of the collector should be concentrated and distributed as uniformly as possible over a discrete area defined by the solar cells, as opposed to the point or line focusing frequently desired for thermal conversion. While the uniform distribution of reflected solar energy over a discrete area can be obtained by carefully defocusing a Fresnel lens or parabolic mirror on a receiver normal to the optical axis, the present invention extends the art to include a receiver parallel to the optical axis, with attendant advantages such as averaging out manufacturing errors.
Our above-identified U.S. Patent is directed to one system employing two reflective surfaces, with a nominal ray crossover point in front of the receiving element, for distributing available energy across the receiving element in a manner to avoid hot-spot problems in a solar cell apparatus. That system also employs a third reflective surface for collecting and re-directing stray energy onto the receiving element to compensate for errors in the reflective surface or the tracking system. While that collecting and concentrating system can be employed with both thermal receivers and solar cells, the apparatus is relatively expensive to manufacture due both to the use of the folded reflective optical system and to the manufacturing tolerances necessary for efficient operation of the apparatus. Accordingly, it is a primary object of the present invention to provide an improved collector of electromagnetic radiation particularly useful in the conversion of solar energy to useful electric energy.
Another object of the present invention is to provide such an improved apparatus which has enhanced performance and durability and in which the optical receiver and protective window are sealed with the receiver inside the enclosure.
Another object of the invention is to provide such an apparatus employing photovoltaic receivers having their receiving surfaces extending substantially parallel to the central axis of the module.
Another object is to provide a compact single reflective, afocal optical system capable of substantially uniformly distributing the concentrated solar energy over a receiver surface.